1. Field of the Invention
The present invention relates to a push button switch, especially to a lateral-push button switch used in small electronic equipment and devices such as mobile phones, portable game devices, digital cameras, mobile personal computers, and so on.
2. Description of the Related Art
A conventional general lateral-push button switch includes a circuit board provided with a fixed contact and a resilient snap dome as a base part, a cover covering the base part of the push button switch and having at a peripheral side surface of the push button switch an opening, and an operating controller inserted in the opening to be disposed slidably in a lateral horizontal direction and configured to press the snap dome toward the fixed contact downwardly (for reference, see Japanese Patent Application Publication Nos. 2006-244977 and 2005-209565).
The base part includes a molded article in which a flat plate-like circuit board or lead frame is formed by insert molding, and the circuit board includes a plurality of solder pads which are provided on a lower surface of the circuit board and electrically connected to the fixed contact and the snap dome. The cover member includes a slope extending inward from an upper part of the cover member, and the slope is inclined to press the operating controller from obliquely above when the operating controller is laterally slid into the push button switch.
When the operating controller is pressed and laterally slid into the push button switch, a leading end portion or inner end portion of the operating controller is downwardly guided and pressed from obliquely above by the slope, and the snap dome comes into contact with the fixed contact.
In this way, by sliding the operating controller in a lateral direction, the snap dome with the fixed contact is configured to execute switch-on and -off operations.
In the push button switch having the aforementioned structure, the cover member is fixed to the base part to cover the snap dome and the fixed contact. The push button switch used in an electronic device is mounted on a motherboard of an electronic device by bonding the base part onto the motherboard directly through soldering.
Because thinning is required in small electronic devices in each of which a push button switch is surface-mounted on a motherboard of the electronic devices, the push button switch is also required to be thin. When the push button switch is surface-mounted on an electronic device, the fixation and the electric connection of the push button switch to the motherboard of the small electronic equipment are simultaneously executed by a reflow process.
However, in the lateral-push button switch having the aforementioned structure, because a user's pushing force on the operating controller that is pressed against the slope of the covering member accompanies performance of the switch-on and -off operations of the snap dome and the fixed contact, it is necessary to increase the strength of the cover member to a certain extent relative to the base part provided with the snap dome and the fixed contact or a motherboard on which the push button switch is finally mounted in an electronic device. In addition, the lateral-push button switch is often installed in small electronic devices such as mobile phones, portable game devices, digital cameras, mobile personal computers and so on as a lateral-push button switch provided at a side surface of the electronic device. However, because a user carries around a mobile phone and other small electronic devices as portable devices, it often happens that the small electronic devices are accidentally dropped or hit on an object, and strong impacts and large stresses often cause problems in the switch function of the push button switch or physical destruction.
In most cases the destruction begins first from a side surface of a cover member, the side surface facing a sliding direction of the operating controller, and thereafter reaches the base part provided with the snap dome and the fixed contact. Therefore, it is necessary to particularly increase strength of a portion of the push button switch close to a switch operation part exposed on a side surface of the mobile phone and other electronic devices.
Furthermore, because the push button switch is finally surface-mounted on the motherboard of an electronic device, it is often bonded by solder in a reflow process. In the reflow process, joint strength tends to increase in proportion to a size of solder-joining area. Therefore, a process of securing a large solder-joining area of the base part of the push button switch to the motherboard has conventionally been executed. However, if the solder-joining area of the circuit board becomes larger, for example, the circuit board and the push button switch become larger which goes against the demand for thinner and smaller push button switches to be mounted in small electronic devices such as mobile phones and other portable electronic devices. Also, if the base part is formed by inserting a lead frame, it is not easy to ensure a large solder-joining area, because a size of electrodes is previously determined.